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Report claims pilots of the Ethiopian MAX 8 followed emergency procedures accordingly
Addis Ababa - The new insights from the investigation of the Ethiopian 737 MAX 8 crash could cause considerable problems for Boeing. (airlinerwatch.com) Mais...
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Great point, we should go all the way back to Boeing's decision to create an airplane the cheapest way possible that appears to be modern with new technology. But in fact it is a collection of a few new parts and mostly old parts made to fit together. And then we should take a look at how this plane made it through certification and made it to the airport accepted by the airlines and their engineers. Then we will know how this got here and more important where we must go now with it, if we want passengers to fly in it.
24000 hours flying 727,757,767,MD 11,DC9,DC8,DC7,DC6,C130, CV440 and I've never been on an airplane that even remotely approached an aerodynamic stall, except on training flights. You would have to be comatose to not feel it in your seat and other cues. Attitudes are so extreme as to be unmistakeable. Only exceptions are T-tailed airplanes that do need power assist on down elevator, but never by trimming stabilizer. Even primary flight students learn stall recovery before solo! Too much unneeded engineering to fix a problem that does not exist. Engineering caused these accidents, not the pilots.
I had been wondering about the need for stall-prevention. Seems that for a very infrequent event, there might be a better way than a blind 'push the nose down' approach. Though, as I recall, the Air France incident resulted from the pilot stalling a perfectly good aircraft right into the drink despite all the stall warnings working well. What really bothers me though is this gorilla system that wrests control from the humans acts decisively based on a single input. I designed avionics in the space industry and we never accepted single point of failure in avionics leading to mission failure unless there was no alternative. Commercial aviation should be at least as conservative. Obviously, since Boeing sells an optional feature for detecting disagreement from two AOA sensors, they could use both as inputs to MCAS. I'm guessing that they could also incorporate airspeed, vertical speed, pitch sensing, and um, I don't know, how about physical principles. In the Ethiopian crash, the AOA sensor showed a near-step function between 11 and >70 degrees up. Physics tells me that this cannot happen and something is broken. Likewise, if the two sensors don't agree, there's a problem. Also, if the aircraft is beginning to stall, the up angle will be accompanied by negative vertical speed derivative. There are many associations which can be checked to verify the actual condition without having to rely on a single sensor. If you're going to design a "safety" device that can crash the plane, at the very least, make sure it uses all available information before doing so.
You people have to understand that the trim activates the horizontal stabilizer which is twice the size of the elevator controlled by the pilot so the pilot cannot overpower the trim when it is active. Now if the aircraft is in a high speed dive after the MCAS has run the trim to full nose down or close to it and is selected off by the pilot, the aerodynamic forces on the stabilizer (trim) are so strong that the pilot cannot override them in manual mode, this probably why they attempted to restart the electric trim in desperation to regain control in this short time event.
A couple other things to add: 1) The horizontal stabs have a "neutral shift" mechanism to the elevators, what this does is move the elevators with the stabs to assist in the pitch trimming, so if the stabs are at full nose down, the elevators are also slightly pitched nose down. 2) The design of the 737 makes the aircraft nose down the faster it is traveling. The 737 has a elevator "mach trim" system that will slightly pitch up the elevators' neutral position to compensate for the nose down tendency at around 250 knots. To summarize, the pilots are fighting a maxed out stab trim which is possibly impossible to roll back by hand cranking (which also would take a long time to do even if it is possible to move), they are pulling back on the yoke as much as possible but not getting the full movement of the elevators due to the neutral shift mechanism, and fighting the natural tendency of the 737 to nose down at high speeds, all within a very short period of time. I, for one, do not blame them in their desperation for turning the cutouts back on in hopes of getting assistance from the electric motors.
I have concluded that both of these 73M accidents were David (the elevator & pilots)) vs. Goliath (the stabilizer & MCAS). Goliath won before David could get the rock out of his pocket. It was a horrendous deadline in the truest sense. I wish the Ethiopians would let the NTSB 'take over'. (I first noticed the 'adjustable' stabilizer on another 'modern' airliner while looking out the window at another plane (a 757 I think) years ago. I was astonished - Holy S*** - the whole d**n assembly goes up and down!).
Remember the rudder nightmare? That also knocked two 737s out of the sky and killed many helpless people. The NTSB eventually found it.
Remember the rudder nightmare? That also knocked two 737s out of the sky and killed many helpless people. The NTSB eventually found it.
As the investigation proceeds, there are a couple of rookie mistakes to watch out for, as even experts sometimes fall into these traps:
1) When analyzing actions and decisions of people over time leading up to an accident, it is unfair to apply your present "perfect" knowledge of what happened. You must "walk the timeline" shoulder to shoulder with those people and assess their actions and decisions with what they knew at that moment in time. Doing the latter can uncover root-cause defects that might otherwise remain undetected.
2) Be careful of firm, unyielding comments about how the systems worked leading up to the accident; e.g., "when you flip this switch, this IS what happened". Everything in the system behavior should now be suspect until the root causes have been identified and fixed; design specifications, test procedures, training, and user documentation has been updated to accommodate new knowledge; and the entire avionics system has been re-validated, i.e., has been shown to meet all design specifications by generating objective evidence from testing, simulations, inspections, and reviews.